Remote testing of telephone loops

Abstract

A telephone subscriber loop testing system is disclosed which can be used for performing standard ringer continuity, noise, leakage, short circuit, and foreign voltage tests over exceptionally long subscriber loops. The sensitivity of the ringer ballistic test is enhanced by placing the reversing switch (which serves to discharge the line) at a location remote from the central office test desk and relatively near to the subscriber station. In one embodiment, the remote ballistic test circuit is incorporated in a remote testing system for a group of subscriber lines connected to the central office through a carrier system. In this embodiment, a separate metallic test path is provided to the remote location which can be selectively connected to any one of a plurality of subscriber loops for such testing.

What is claimed is: 
     
       1. A ringer continuity test circuit for a telephone loop comprising a source of direct current test voltage at a central location;   a line reversal switch connected in said telephone loop at a location remote from said central location;   means for operating said line reversal switch: and   metering means for indicating current level changes in said loop.   
     
     
       2. The ringer continuity test circuit of claim 1 wherein said means for operating said line reversal switch includes means responsive to said direct current test voltage.   
     
     
       3. A ringer continuity test circuit for a subscriber loop carrier system comprising a source of direct current test voltage at a central location;   a metallic test path from said central location to the remote terminal of said carrier system;   means for selectively connecting said metallic test path to a local subscriber loop at said remote terminal;   line reversal means in said metallic test path at said remote terminal location; and   means for detecting current changes in said metallic test path.   
     
     
       4. The ringer continuity test circuit according to claim 3 wherein said line reversal means includes means responsive to said direct current test voltage to reverse the connection to said local subscriber loop after a preselected delay interval.   
     
     
       5. The ringer continuity test circuit according to claim 3 further including a multifrequency line identification signal source; and   multifrequency detector means responsive to signals from said multifrequency source for enabling said selective connecting means.   
     
     
       6. A testing system for telephone lines connected to a central office through a carrier system comprising a test desk including a current detector at the central office end of said carrier system;   a common loop testing circuit at the remote end of said carrier system;   a metallic path extending from said test desk to said common loop testing circuit; and   line reversal means in said common loop testing circuit.   
     
     
       7. The testing circuit according to claim 6 further including means for selectively connecting metallic telephone loops at said remote end of said carrier system to said common loop testing circuit.   
     
     
       8. The testing circuit according to claim 7 further including means responsive to said selective connecting means for interposing said common loop testing circuit between said metallic telephone loops and said carrier system; and   means utilizing said metallic path for conducting alternating current tests of said carrier system.